1. Field of the Invention
The present invention relates to a clamping apparatus of the screw engaging type, and more specifically to a clamping apparatus of the type adapted to fixedly secure a metal mold and the like to a base by screwing and threadably engaging an external thread of a clamp rod with an internal thread formed in the metal mold and the like.
2. Description of Prior Art
As such apparatus there has been known the one, for example as disclosed in the Japanese Utility Model Publication No. 49-36057.
In this apparatus, while a connecting internal thread is formed in a member to be fixed such as a metal mold, a raising and lowering internal thread is formed in a base. A clamp rod is threadably engaged over both these internal threads and adapted to be rotated by an electric motor fixed to the base.
There are, however, following problems associated with the above-mentioned conventional apparatus.
Although the member to be fixed and the base are connected by the clamp rod, since a screw clearance exists between the connecting internal thread of the member to be fixed and the external thread of the rod and a screw clearance exists also between the raising and lowering internal thread of the base and the external thread of the rod, the force which pulls the member to be fixed and the base against each other can be hardly produced between them. Therefore, that conventional clamping apparatus should be called a coupling apparatus rather than the clamping apparatus.
Further, due to the error occuring when the member to be fixed is placed onto the base, an axis of the connecting internal thread and an axis of the raising and lowering internal thread happen to be misaligned. In this case, since the external thread of the clamp rod can not be engaged readily with the connecting internal thread, these threads would be damaged by a forcible engagement.